The invention herein described relates generally to a system and method for measuring an interrupted surface and, more particularly, to a system and method for measuring an interrupted surface while selectively excluding certain interruptions in or on the surface.
Many mechanical systems (e.g., automobile engines) utilize components of precise dimensions and tolerances which require meticulous quality control and inspection to achieve such dimensions and tolerances in order to ensure proper fit and operation. For many objects, measurement of true flatness, roundness, parallelism and the like, or variance therefrom is usually a necessary and often critical requirement. There are various devices for such measuring which generally utilize a probe element that measures variances, or the maximum and minimum height, in the surface of the object. The variance is typically sensed by mechanical means to provide an electrical signal which is proportional to the variance.
Oftentimes, the surface includes one or more cut-outs or raised portions commonly referred to in the art as surface interruptions, which the probe detects and undesirably includes in the data used to determine the surface variances. One such example is in a run-out measurement of the surface of a cylinder having one or more oil slots. The oil slot disrupts the measurement of the surface so that instead of measuring variation in the surface, the probe measures the depth of the oil slot.
Attempts heretofore have been made to measure the maximum and minimum regions in the surface while excluding the interruptions. Thus, others have attempted to exclude an interruption by including some means of identifying the location of the interruption before making the surface measurement. For example, a technician may use a mechanical device such as a mechanical stop wherein, as the object is turned or otherwise moved, the probe element detects that it is approaching the mechanical device and therefore stops taking data. The probe would then exclude data measured for the duration that it detects the mechanical stop. This method is inconvenient and inefficient since it requires the technician to expend time to determine the location of the slot or other interruption and install a stop mechanism prior to making the surface measurement.
Another way of determining the surface of an object having interruptions is to use a position encoder to xe2x80x9ctrackxe2x80x9d the position of the object and exclude measurements over a predetermined range on the surface of the part (e.g., excluding measurements taken between 0 and 10 degrees of a cylindrical part as it is rotated). One disadvantage to this method is that if the size of the object varies and the position of the interruption varies from one part to the next, the interruption may fall outside the predetermined range and result in an inaccurate surface measurement. In this regard, oftentimes the interruption is formed in the surface of a part that is then welded to another object. For example, an oil slot may be cut into a bearing that is then welded to the cylinder. The technician may weld the bearing in a position different from that of a previous weld which, again, may create inconsistencies and/or inaccuracies in the surface measurements.
Another disadvantage of excluding interruptions over a predetermined range is that oftentimes the edges of the interruption may fall outside of the range and cause inaccuracies in the measured surface readings. In many cases, the edges of an interruption are the most critical region to include in a surface measurement. In this regard, oftentimes when a cut is made in an object, such as in a cylinder, an abnormality may form at the cut-edge and therefore should be included in the surface measurement indicating a defective cylinder surface.
Still others have attempted to create a profile of the object by, for example, using a detector to actively profile the object. According to this method, every data point is correlated with its previous and/or subsequent data point to determine their relationship to one another and then stored in the memory of a computer for subsequent processing. This method suffers from at least two drawbacks. First, it is limited by the amount of memory available to which the detector is connected. Second, the results are not real-time in the sense that the profile data require after-the-fact analysis to determine the surface measurement.
Consequently, it would be desirable for a system and method that accurately measures a surface while accurately excluding interruptions in the surface.
The present invention provides a system and method for diagnosing and measuring surface imperfections of an article in real time. The invention excludes unwanted surface interruptions in an efficient way requiring little or no user intervention. More particularly, the present invention excludes surface interruptions by employing a real time sampling system to determine high and low regions in a raised surface and excluding regions in a depressed or lower surface. The present invention determines high and low regions by detecting peak data changes in an incoming set of data. By detecting changes in peak data, minimal memory is required allowing an infinite number of surfaces to be measured over an infinite number of surface interruptions. The surface measurements are resolved in the sampled time period without maintaining historic data samples from previous surface measurements.
One particular aspect of the invention is characterized by a data collection system for collecting data relating to a surface of an article, and a processor operatively coupled to a data collection system for analyzing the surface data to determine deviations in the surface corresponding to surface imperfections and pre-made surface interruptions, and distinguishing between the imperfections and interruptions.
According to yet another aspect of the invention, a method and system for diagnosing surface imperfections of an article is provided. The system is characterized by a means for collecting data values corresponding to levels in the surface, and means for comparing data values corresponding to surface maximums to determine an overall maximum height in the surface and comparing data values corresponding to surface minimums to determine an overall minimum height in the surface. Also, means are provided for setting the overall maximum height equal to a most recent surface maximum data value unless a previous data value is greater. In a similar manner, means are provided for setting the overall minimum height equal to a most recent surface minimum data value unless a previous data value is lower.
According to yet another aspect of the invention, a system for determining run-out in the surface of a cylinder having one or more oil cut slots in its surface is provided. The system is characterized by a probe for collecting data relating to the surface of a cylinder and a controller for analyzing a data value if it corresponds to a portion of the surface between the oil cut slots and excludes a data value if it corresponds to a portion of the surface in, or within a predetermined area of, the one or more oil cut slots. The controller is operative to update a current maximum data value with a subsequent data value if the subsequent data value exceeds the lowest minimum data value between the current and subsequent data values plus a predetermined acceptable noise margin. The controller is further operative to update a current minimum data value with a subsequent data value if the subsequent data value falls below the highest maximum data value between the current and subsequent readings less the predetermined acceptable noise margin.
The foregoing and other features of the invention are hereinafter fully described. The following description and the annexed drawings setting forth in detail one or more illustrative embodiments of the invention, such being indicative, however, of but one or a few of the various ways in which the principles of the invention may be employed.